Recent content by Robert_G

Hi, there. I don't understand how the light travel in the medium which has the index of refaction below one from the following topic: http://en.wikipedia.org/wiki/Total_external_reflection “For X-rays, however, all materials have indices of refraction slightly below 1. ” I did some...

It's a rough journey to learn this things, oh, my brain.

Hi there: I am reading a book (Atom-Photon interaction by Claude Cohen-Tannoudji, Page 448) and the following things gave a big headache. (1) Is there a density equation in Schrödinger Picture. because I encounter one, like: ##i \hbar \frac{d \sigma}{dt}=[\hat{H}, \sigma]## and...

[A,B]=0? Am i right?

Can you tell me why?

The same thing as title.

In a book called quantum optics by M.O.Scully, the eigen-state of the operator ##a## is written as ##|\alpha\rangle##, Here, in the book by Claude. the eigen-state is ##|\alpha \exp(-i\omega_L t)\rangle##. This is the same thing. The latter is just using the form of ##\rho e^{i \theta}## to...

Hi, there. The following is copied from a book " atom-photon interaction " by Prof. Claude Cohen-Tannoudji, Page 415. I do not understand it at all. I do know some thing about the coherent state. such as ##a |\alpha\rangle = \alpha |\alpha\rangle## and ##|\alpha\rangle =...

If formula (2) is already the exact solution. It should contain all the information, why we still iterate it to get the perturbation. It does not make sense to me.

hi there; I need some help with the following formulas In the interaction picture. ##\frac{d}{dt}\rho(t)=\frac{1}{i\hbar}[V(t),\rho(t)]## (1) Then ##\rho(t+\Delta t) = \rho(t)+\frac{1}{i\hbar}\int_t^{t+\Delta t} dt' [V(t'),\rho(t')]## (2) This equation can be iterated. and...

Hi, there I am reading the book called "Atom-Photon Interaction", the chapter of " Radiation considered as a Reservoir". My question is actually short, but I have to describe the background. Following is the density equation which describes the interaction between the damped harmonic...

Thank all of you. very happy to find this forums.

I might get a little closer, we can just write ##\hat{\rho}=0.3|a_1\rangle \langle a_1|+0.7|a_2\rangle \langle a_2|## and this ##\hat{rho}## is not an outer product of any vectors in the Hilbert space, because it is a classic statistic thing, right? and How can we create a mix state...

Is this correct? This is the one who start this discussion. After I read the above replies, I try to think it by myself. and let's see whether I got it right? Density operators are used to describe system (A) that is composed by some subsystems (a1, a2, a3...ai...). The mechanics that the...

Hi, there. I am a little confused about the following statement in Wikipedia. and it's about the density operators. "...As mentioned above, a state of a quantum system is given by a unit vector in a Hilbert space. More generally, if one has a large number of copies of the same system, then...